As non-destructive deterioration diagnosis method for a prestressed concrete utility pole, an electrode is connected to an edge position of a tension bar thereof, a counter electrode is contacted on a side face of a position to be inspected, and an amount of moisture in the concrete is estimated from the impedance characteristic. Thus, a hydrogen concentration in the steel material is estimated as a standard for brittle fracture of the tension bar. In this method, the electrode needs to contact near the position to be inspected. Accordingly, in order to inspect all regions of the utility pole, all surfaces of the utility pole needs to be scanned by the electrode, and burden for the inspection is very large.
As another method, velocity tomography method is well known. In this method, elastic waves are occurred by striking a predetermined portion of the concrete, the elastic waves (propagated inside the concrete) are detected by an elastic wave sensor (AE sensor), and a distribution of elastic wave velocity (as a standard for deterioration and damage position inside the concrete) is estimated from a travel time of the elastic waves to the sensor. In the velocity tomography method, an adhesion is mainly used to attach the sensor. However, the adhesion is hard to attach and remove a plurality of sensors in a short time. Furthermore, in the case of fixing such as binding a measurement target with a band, the pressure-bonding force has dispersion, and the elastic waves cannot be suitably detected. Furthermore, in order to analyze the distribution of elastic wave velocity, an excitation position and an attachment position of AE sensor need to be correctly determined. However, the target position is not previously determined. Accordingly, the excitation position and the attachment position cannot be correctly determined.